1. Field of the Invention
The present invention relates to isolated sampling of differential input signals. In particular, the present invention relates to isolated sampling of differential input signals in a sampling network, such as an input stage of an analog-to-digital converter (ADC).
2. Discussion of the Related Art
FIG. 1 is a schematic diagram of a differential double-correlated sampling instrumentation amplifier (circuit 100) disclosed in the article (“the Yen article”), entitled “A MOS Switched-Capacitor Instrumentation Amplifier,” by R. C. Yen and P. R. Gray, published in the IEEE Journal of Solid State Circuits, pp. 1008-13, December, 1982. As shown in FIG. 1, circuit 100 of FIG. 1 shorts the input terminals VIN+ and VIN− with switch S3 that is controlled by a signal φ2. Signal φ2 is a logic signal that swings within the power supply voltages. As circuit 100 does not use charge pumps for controlling the input sampling network, circuit 100 is unable to sample far outside of the power supply voltages.
FIG. 2 shows a prior art ADC driver circuit that receives a single-ended input signal to provide a differential signal for an ADC. As shown in FIG. 2, the ADC driver circuit requires resistive dividers and an additional buffer amplifier to limit the differential voltage at the ADC input terminals to a voltage swing that is close to that of the ADC's supply voltages.